Comprehensions

Comprehensions are simple, but powerful, syntaxes that allow us to transform or filter an iterable object in as little as one line of code. The resultant object can be a perfectly normal list, set, or dictionary, or it can be a generator expression that can be efficiently consumed while keeping just one element in memory at a time.

List comprehensions

List comprehensions are one of the most powerful tools in Python, so people tend to think of them as advanced. They're not. Indeed, we've taken the liberty of littering previous examples with comprehensions, assuming you would understand them. While it's true that advanced programmers use comprehensions a lot, it's not because they're advanced. It's because a comprehension is so fundamental to Python, it can handle many of the most common operations in application software.

Let's have a look at one of those common operations; namely, converting a list of items into a list...